The present invention relates to the formulation of an antiplaque dentifrice with improved foaming, improved taste, solubilized active ingredient, improved fluoride stability, improved compatibility of all components, improved extrusion characteristics from various containers and increased cost effectiveness.
Until now it had been difficult to formulate a cosmetically acceptable antiplaque dentifrice consisting of a quaternary ammonium compound and a betaine surfactant with a humectant system of all glycerin or all sorbitol. In addition, the use of mixtures of glycerin/polyethylene glycol or sorbitol/polyethylene glycol, where glycerin or sorbitol were present in excess of 10% by weight of the formulation, displayed marginal cosmetic stability. However, after extensive solubility tests on various mixtures of the components in the benzethonium chloride (BTC) dentifrice, a compatible system of water, BTC, betaine, salts and glycerin was found which was dependent upon the order of addition of these components.
Accordingly, it has been found that by using a specific process, stable formulations of an antiplaque dentifrice containing a quaternary ammonium compound and a betaine surfactant can be made with glycerin or sorbitol as the humectant. The essential features in this process is the formation of two separate phases with the subsequent combination of these two phases to form the stable system. One of these phases contains the active quaternary ingredient (benzethonium chloride or cetyl pyridinium chloride) solubilized in the betaine surfactant (cocamidopropyl betaine) and a flavor, which is designated the oil gel phase. The second phase contains water, humectant, and nonionic gelling agent e.g. hydroxyethylcellulose, and optionally sodium saccharin and fluorine-containing compound i.e. sodium monofluorophosphate, and is designated to the water gel phase. The dental polishing agent may be added to the combined phases as a final step, or be added to the water gel phase prior to combining with the oil gel phase. The finished product has improved chemical and cosmetic stability and improved taste.
A conventional method of preparing antibacterial dentifrices containing a quaternary ammonium compound as the active material is disclosed in U.S. Pat. Nos. 4,118,476 and 4,188,372, and comprises the formation of a gel with humectant (glycerin, sorbitol, polyethylene glycol), thickener (hydroxyethylcellulose), and sweetener, and adding thereto polishing agent, flavor, antibacterial agent, additional water, and lastly an antistain agent (a phosphono-containing compound or a mellitic acid-containing compound).
The prior art also discloses processes for stabilizing a dentifrice against precipitation and floculation due to the incompatibility of an antibacterial agent and an alkali metal carboxyalkyl cellulose, as shown in U.S. Pat. Nos. 3,842,168 and 3,843,779. The former patent utilizes the steps of adding the antibacterial agent dissolved in water to a non-aqueous blend of the carboxymethylcellulose, sodium saccharin and humectant and then adding the surfactant to form a gel, to which is added the polishing material and flavor as a final step. The latter patent adds the antibacterial agent separately or cojointly with the surfactant to a mixture of glycerin, water, sodium saccharin, carboxymethylcellulose and surfactant, followed by the addition of a polishing material and flavor. The addition of the surfactant must precede or be simultaneous with the antibacterial addition in order to avoid precipitation in the dentifrice.
However, the prior art does not disclose a cosmetic, and chemically stable antiplaque dentifrice containing as the essential ingredients, a quaternary ammonium antiplaque compound, a zwitterionic betaine surfactant, a glycerin and/or sorbitol humectant, and a nonionic gelling agent prepared by a novel process utilizing a specific sequence of steps, which comprises the formation of two separate gel phases, an oil gel phase consisting of the quaternary ammonium compound, betaine surfactant and flavor; and a water gel phase consisting of water, humectant and gelling agent; combining the two gel phases into a single parent gel, and adding a dental abrasive to the combined gel phase as a final step or to the water gel phase prior to the addition of the oil gel phase.